Subject: Re: [RFC PATCH v3 net-next 6/7] net: ethtool: add a mutex protecting RSS contexts

From: "Russell King (Oracle)" <[email-masked]>
Date: Tue, 12 Sep 2023 17:40:25 +0100

On Tue, Sep 12, 2023 at 03:21:41PM +0100, [email-masked] wrote:
> From: Edward Cree <[email-masked]>
> 
> While this is not needed to serialise the ethtool entry points (which
>  are all under RTNL), drivers may have cause to asynchronously access
>  dev->ethtool->rss_ctx; taking dev->ethtool->rss_lock allows them to
>  do this safely without needing to take the RTNL.
> 
> Signed-off-by: Edward Cree <[email-masked]>
> ---
>  include/linux/ethtool.h | 3 +++
>  net/core/dev.c          | 5 +++++
>  net/ethtool/ioctl.c     | 7 +++++++
>  3 files changed, 15 insertions(+)
> 
> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
> index 8977aa8523e3..1f8293deebd5 100644
> --- a/include/linux/ethtool.h
> +++ b/include/linux/ethtool.h
> @@ -1026,11 +1026,14 @@ int ethtool_virtdev_set_link_ksettings(struct net_device *dev,
>  /**
>   * struct ethtool_netdev_state - per-netdevice state for ethtool features
>   * @rss_ctx:		IDR storing custom RSS context state
> + * @rss_lock:		Protects entries in @rss_ctx.  May be taken from
> + *			within RTNL.
>   * @rss_ctx_max_id:	maximum (exclusive) supported RSS context ID
>   * @wol_enabled:	Wake-on-LAN is enabled
>   */
>  struct ethtool_netdev_state {
>  	struct idr		rss_ctx;
> +	struct mutex		rss_lock;
>  	u32			rss_ctx_max_id;
>  	u32			wol_enabled:1;
>  };
> diff --git a/net/core/dev.c b/net/core/dev.c
> index f12767466427..2acb4d8cd4c7 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10054,6 +10054,7 @@ int register_netdevice(struct net_device *dev)
>  	idr_init_base(&dev->ethtool->rss_ctx, 1);
>  
>  	spin_lock_init(&dev->addr_list_lock);
> +	mutex_init(&dev->ethtool->rss_lock);

Is there a reason to split this from the idr (eventually xarray)
initialisation above? Surely initialisations for a feature (rss)
should all be grouped together?

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